Production oil wells typically contain a well casing into which is inserted a production tubing string. The production tubing string serves as both a means to insert and remove a downhole pump and pump rod, and provides a conduit for the extraction of oil and fluids from the well. The upper end of the production tubing string is held within the well casing through the use of a variety of flanges, hangers, rotating heads, or similar devices. Attached at or near the lower end of the tubing string is a downhole pump that is most commonly either a reciprocating or a progressive cavity pump. Reciprocating pumps are traditional oil well pumps wherein the pump rod is reciprocated within the production tubing string by means of a pump jack or similar device. In progressive cavity pumps the pump rod is attached to a downhole rotor that is confined within a pump housing such that rotation of the pump rod causes the rotor to rotate and pump or drive oil and other fluids to the surface.
Regardless of the form or type of downhole pump utilized within the oil well, it is necessary to securely anchor the lower end of the production tubing string to the well casing. Anchoring the lower portion of the tubing string serves to hold it in place so that downhole equipment and the interior surface of the well casing are not damaged during operation as will be the case if the production tubing string were merely allowed to be suspended freely within the well casing. In addition, the downhole anchoring device serves to prevent the production tubing string from moving upwardly or downwardly, in the case of reciprocating pump, or from rotating, in the case of a progressive cavity pump, during pumping.
While others have proposed downhole anchoring devices having a variety of different configurations and methods of operation, existing anchors all suffer from a number of common limitations. First, many are mechanically complex and involve complicated and expensive mechanical structures in order to "set" them and anchor the production tubing string to the well casing. Many other current downhole anchors are severely limited in terms of their application in oil wells having a high sand content. In cases where oil is contained in sand formations, during production sand can often become tightly packed around the anchor making it difficult, and in some cases impossible, to release the anchor and remove it from the well when desired. Where the anchor fails to release, laborious and expensive flushing procedures must be employed in order to wash compacted sand from around the anchor allowing it to release. High pressure or sour gas wells add additional complications under such circumstances. Finally, prior downhole anchors have herebefore not provided a mechanism by which the production tubing string can be released from the anchor in the event that the anchor becomes jammed or sanded in while in its deployed state.